Comparison of the Peak Inspiratory Pressure and Lung Dynamic Compliance between a Classic Laryngeal Mask Airway and an Endotracheal Tube in Children Under Mechanical Ventilation.

Background
The present study was performed with the aim of comparing the peak inspiratory pressure and lung dynamic compliance between a classic laryngeal mask airway (LMA) and an endotracheal tube in children under mechanical ventilation.


Materials and Methods
In this study, 30 children aged 1 to 7 years with a physical condition of ASA I-II who were admitted for operations to repair inguinal hernias, hydroceles, or hypospadias were randomly enrolled. After induction of anesthesia, the appropriate laryngeal mask was used for each patient and they were placed under pressure-controlled mechanical ventilation. The peak inspiratory pressure was adjusted and recorded to obtain an appropriate tidal volume, then the laryngeal mask was removed and the appropriate size uncuffed endotracheal tube was inserted and the patient was placed again under controlled mechanical ventilation. The required settings were adjusted and peak inspiratory pressure and tidal volume were measured and recorded by the ventilator. Dynamic compliance was also calculated in both cases using the appropriate formula.


Results
The results showed that peak inspiratory pressure (PIP) with the use of LMA in children under mechanical ventilation was less than the PIP with the use of an endotracheal tube (p<0.05). Also, the pulmonary dynamic compliance with a laryngeal mask was greater than the use of an endotracheal tube (p<0.05).


Conclusion
A laryngeal mask airway due to its low airway resistance and high dynamic compliance is an acceptable alternative to a tracheal tube during mechanical ventilation and it can be a good alternative to the endotracheal tube, especially during mechanical ventilation of children, in whom avoidance of barotrauma is desirable.

The laryngeal mask airway (LMA) is the best supraglottic device currently used in airway management and comes in sizes 1-6 for use from neonates to adults with more than 100 kg of weight (6). Also, LMA is able to provide airway management in infants and children. Its use is contraindicated in patients with a risk of aspiration of gastric contents, but if it is chosen and placed correctly and mechanical ventilation is adjusted with positive pressure volumes (PPV) less than 10 mg/kg, almost no episodes of gastric distention will be observed. Safe use of PPV with LMA at different ages has been confirmed (9).
Compared to the endotracheal tube, LMA has advantages such as less manipulation of the airway and easier application and it is a good alternative to the endotracheal tube, especially in short-term surgery. LMA is less invasive and results in less postoperative discomfort. In addition, during its use, there are significantly fewer hemodynamic changes compared to the use of endotracheal tubes (ETT) (10).
In a comparative study, it was shown that LMA provides appropriate airway management in more than 90% of infants and children. No differences were observed between LMA and the endotracheal tube in complications such as laryngitis, bronchospasm, or increased saliva.
Coughing and holding the breath were observed at lower rates in the use of LMA (9). In a study of children aged 2-10 years (with a weight of 10-20 kg), in order to assess breathing with positive pressure and the use of LMA or ETT, it was observed that application of the LMA was easier than inserting an ETT, and hemodynamic changes, airway complications, and soft tissue trauma were significantly less with the use of LMA (10). In another study on adults under undergoing orthopedic surgery that was performed in Iran, it was found that LMA creates higher resistance and lower dynamic compliance than ETT (11). In the studies performed, it was specified that in the case of mechanical ventilation with the LMA, the inspiratory pressure should be less than 20 cm H2O; if it is higher, the risk of inflation of the stomach and regurgitation increase, especially when the LMA is not inserted correctly, and this occurs more frequently with the use of size 1 and 1.5. Compared to the controlled volume mode, pressure controlled ventilation reduces the required inspiratory pressure and it can improve ventilation distribution in infants and children (12). Also, in a comparative study on mechanical ventilation with LMA and an uncuffed endotracheal tube in children weighing less than 30 kg, in the cases of older children, LMA with a size larger than 2.5 was inserted and air leaks compared between LMA and ETT were similar, but it was not recommended to use LMA in children weighing less than 10 kg (13).
Today, reducing airway resistance and improving dynamic compliance during mechanical ventilation are desirable goals to control hemodynamic status and to prevent pulmonary barotrauma, especially in children (11).
Therefore, it is necessary to work toward the use of lower inspiratory pressure and airway resistance and higher compliance during mechanical ventilation in children.

RESULTS
In the present study, 30 boys with a mean age of 2.98  1.23 and mean weight of 13.78  3.20 kg were studied.  (Table 1).
Also, the results showed that lung dynamic compliance with the use of LMA was greater than the lung dynamic compliance with the use of an endotracheal tube (P  0.05) ( Table 1).

DISCUSSION
LMA is an appropriate non-invasive alternative to an endotracheal tube, and it is an acceptable method during a short-term operation and in cases where intubation is difficult. Because there is no need for laryngoscopy, it does not have many adverse consequences related to its use. In another study on 60 children under general anesthesia, the respiratory parameters during ventilation with positive pressure with LMA vs an endotracheal tube were compared with each other. No differences were observed between the two groups in terms of inspiratory pressure, tidal volume, or leakage of gas but a significant difference was observed between them in terms of airway resistance and pulmonary compliance, and LMA was superior. This result is consistent with the results of the present study (16).
Idrees and Khan also compared LMA and endotracheal tubes during mechanical ventilation in adults undergoing peripheral limb surgery. The results showed that the hemodynamic changes during insertion of the tube with the LMA was lower but no significant difference was observed in terms of cardiac effects during extubation. The incidence of cough and mild hypoxemia during extubation with the endotracheal tube was higher. Therefore, an LMA is more appropriate for mechanical ventilation in selected patients (17).  (18).
According to the results of the Asida and Ahmed study, the use of LMA is a reliable ETT alternative in pediatric patients due to its low failure rate and ease of insertion (19).
In another study on adults undergoing orthopedic surgery, which was performed in Iran, it was found that an LMA creates higher resistance and lower dynamic compliance than ETT (11). This result is inconsistent with the results of the present study. The advantages of LMA in children aged under 12 years were investigated and compared to ETT. The results of 16 clinical trial studies were analyzed. The results showed that compared to ETT, LMA has three advantages: a lower incidence of cough while awake, a lower prevalence of sore throat and nausea after surgery, and no significant difference was observed between them in terms of laryngitis and bronchospasm (20). Also, in another study by Genzwuerker et al., LMA was introduced as an effective device in airway management. The results of both studies are consistent with the results of the present study (21).
It seems that the reasons for the inconsistency in the results of some studies are the duration of anesthesia and the studied population. Our study has some limitations.
The studied children were ASA I-II and therefore our results cannot be extended to patients with previous respiratory disease or obesity. In addition, the duration of surgery was short.

CONCLUSION
It can be concluded that LMA is an acceptable alternative to an endotracheal tube, especially during short-term operations in children due to lower airway resistance and higher dynamic compliance, and prevention of intubation complications such as cough, less stress on the patient, and as a result, better control of the patient's hemodynamic responses (22). Therefore, we suggest future studies examine the use of LMA in various surgical procedures with a longer duration and be performed in various positions, and also in patients with pulmonary disease and in the intensive care unit.